An Orthotropic Nonlinear Thermoviscoelastic Model for Polymeric Battery Separators

Abstract

Structural responses of separators are critical to battery safety. Commonly used separators are dry-processed polymers with anisotropic microstructures. Due to the material anisotropy, rate dependence, and temperature dependence, developing a model for predicting the thermomechanical response of polymeric battery separators has been challenging. This paper presents an orthotropic nonlinear thermoviscoelastic model for predicting the response of polymeric battery separators in thermal ramp scenarios. The model was based on the Schapery nonlinear viscoelastic model and the temperature dependence was introduced through the time-temperature superposition principle (TTSP). The model was implemented in LS-DYNA® finite element (FE) package as a user-defined material model. The model parameters were determined for a polypropylene (PP) separator. The predicted material responses under large deformations in isothermal and non-isothermal temperature conditions for stress relaxation, creep and tensile loadings at different rates agree well with the experimental data.